AgX should not be written in lowercase letters

This name is taken for the new tonemapper from pseudo-chemical notation,
where it is written as AgX. This is quite different from, for example,
the name "sigmoid", which is originally just an adjective, so it can
easily obey our style. agx forced into lowercase looks extremely strange.

Author: victoryforce

data/darktableconfig.xml.in

@@ -3614,7 +3614,7 @@
       <enum>
         <option>scene-referred (sigmoid)</option>
         <option>scene-referred (filmic)</option>
-        <option>scene-referred (agx)</option>
+        <option>scene-referred (AgX)</option>
         <option>display-referred (legacy)</option>
         <option>none</option>
       </enum>

src/iop/agx.c

@@ -41,7 +41,7 @@ DT_MODULE_INTROSPECTION(6, dt_iop_agx_params_t)
 
 const char *name()
 {
-  return _("agx");
+  return _("AgX");
 }
 
 const char *aliases()